Name: _____KEY______________________________
Date: ________________
Period: ______
WS Acid-Base Titration Curves
(simulated lab with data)
1. Use the titration curves on page 5 to identify the types of acid and base present in the two
experiments, A and B. Justify your answers.
A)
SA w/ SB b/c:
-very low initial pH (~1)
-level increase in pH (not gradual)
-steep/rapid increase in pH at Veq
-very high final pH (~13)
B)
WB w/ SA b/c:
-moderately high initial pH (~11)
-gradual decrease in pH (not level)
-subtle decrease in pH at Veq
-very low final pH (~1)
2. Assuming 10 mL of initial analyte and a reacting ratio of 1:1 in each case, calculate the
concentration of solution A and the concentration of solution B.
A
B
25
___mL
added of
____M
0.1
_____
HCl titrant
25
___mL
added of
0.1
NaOH titrant
____M
_____
10 mL titrated of
____M
0.25 _____
B analyte
10 mL titrated of
A analyte
____M
0.25 _____
0.025 L NaOH x 0.1 mol NaOH x 1 mol A = 0.0025 mol A
1 L NaOH 1 mol NaOH
0.0025 mol A = 0.25 M A
0.010 L A
0.025 L HCl x 0.1 mol HCl x 1 mol B = 0.0025 mol B
1 L HCl
1 mol HCl
0.0025 mol B = 0.25 M
1B
0.010 L B
3. Answer the following questions regarding the concentrations of bases used in titrations.
a) A volume of 30.0 mL of 0.25 M HCl neutralizes a 50.0 mL sample of KOH solution.
What is the concentration of KOH ?
HCl + KOH  H2O + KCl
0.0300 L HCl x 0.25 mol HCl x 1 mol KOH = 0.0075 mol KOH
1 L HCl
1 mol HCl
0.0075 mol KOH = 0.15 M KOH
0.0500 L KOH
b) A volume of 50.0 mL of 0.30 M HCl neutralizes a 50.0 mL sample of Ca(OH)2 solution.
What is the concentration of Ca(OH)2 ?
2 HCl + Ca(OH)2  H2O + 2 CaCl2
0.0500 L HCl x 0.30 mol HCl x 1 mol Ca(OH)2 = 0.0075 mol Ca(OH)2
1 L HCl
2 mol HCl
0.0075 mol Ca(OH)2 = 0.15 M Ca(OH)2
0.0500 L Ca(OH)2
4. What is the difference between the terms strength (strong or weak) and concentrated (diluted or
concentrated) when referring to acids?
Strength is determined by Ka and % ionization of the molecules of a substance.
(i.e. how far a reaction of acid molecules proceeds to the right to make ionized products)
Concentration is determined by the molarity or the moles of acid molecules in solution.
Strength and Concentration are related concepts, but not the same concept.
One could have a concentrated (many molecules) acid that is weak (doesn’t ionize much), or
one could have a dilute (small amount of molecules) acid that is strong (all the molecules
present are ionized).
2
5. Complete the titration curves below. In each case the base is added to a starting volume of
25.0 mL of the weak acid, each have the same concentration, and each react in a 1:1 ratio.
Strong base added to a weak acid
Veq
Volume of base added (mL)
Strong acid added to a weak base
Veq
Volume of base added (mL)
3
6. The figure below shows the variation of pH on titrating 25.0 mL of 0.100 M NaOH with a
monobasic acid (one with only one hydrogen ion) HA. The reaction takes place in a 1:1 ratio.
a) Estimate the pH of the solution at the equivalence point and suggest a suitable indicator for
the titration.
pH ~ 8.5 , phenolphthalein
(which changes color between pH 8-10 & has a pKa ~ 9)
b) Is the acid strong or weak?
weak
(at Veq, pH > 7 indicating the presence of a weak conjugate base)
c) What volume of acid is needed to neutralize all of the sodium hydroxide?
20.0 mL
(rapid decrease in pH at V = 20.0 mL shows equivalence occurred)
d) Write an equation for the reaction taking place and calculate the molarity (concentration) of the
acid.
HA + NaOH
H2O + NaA
or
HA + OH–
H2O + A–
0.0250 L NaOH x 0.100 mol NaOH x 1 mol HA = 0.00250 mol HA
1 L NaOH
1 mol NaOH
0.00250 mol HA = 0.125 M HA
0.0200 L HA
4
Titration Curve for Solution A
14.00
12.00
10.00
8.00
pH
6.00
4.00
2.00
0.00
0
10
20
30
40
50
60
50
60
Volume of 0.1 M NaOH added (mL)
Titration Curve for Solution B
12.00
10.00
8.00
pH 6.00
4.00
2.00
0.00
0
10
20
30
40
Volume of 0.1 M HCl added (mL)
5